Iron casting is one of the most ancient casting technologies in the world. The iron castings are made by melting and pouring into molds or castings to make a part of the product with a certain size and form. The method to make iron castings is used in many different industries. In the manufacturing process of iron castings, alloy elements determine the type of cast iron. Although both steel and cast iron contain trace amounts of carbon and look similar, there are significant differences between the two metals. The carbon content in the steel is less than 2%, which allows the final product to solidify in a single crystalline structure. Cast iron is excellent for casting due to its high carbon content and the presence of silicon.
Iron Castings can be divided into a few categories such as Grey, Ductile, White, Malleable, Compacted graphite, and others. Let’s take a closer look at each type.
White iron casting
Carbon atoms combine with iron to form iron carbide with the right carbon content and high cooling rate. This means that the cured material contains only a few free graphite molecules. The cross-section appears white when the white iron is sheared since there is no graphite. The structure of the cementite microcrystalline is hard but fragile with high compressive strength and good wear resistance. It is desirable to have white iron on the product surface in some specialized applications. This can be achieved by using good thermal conductors to make part of the mold. This will quickly extract heat from the molten metal from that particular area, while the remaining iron castings will cool at a slower rate. One of the most popular grades of white iron is nickel hard iron. The addition of chromium and nickel alloys gives this product excellent performance in low impact, sliding friction applications.
● High compressive strength
● Difficult to machine
● Good hardness
● Resistance to wear
Grey iron casting
The composition of gray cast iron is different its counterparts as it resembles small flakes. When this metal is fractured, the break occurs along with the graphite flakes, which gives it the grey color on the fractured metal’s surface. The name grey iron comes from this characteristic.
By adjusting the cooling rate and composition, the size and matrix structure of flakes can be controlled during the production process. The tensile strength of grey cast iron is lower than that of other cast iron and the ductility is also lower. On the plus side, it is a better thermal conductor and has a higher level of vibration reduction. Its damping capacity is 20–25 times that of steel and is superior to all other cast irons. Grey iron is also easier to machine than other cast irons, and its wear resistance makes it one of the highest cast iron products.
● Good machinability
● Good resistance to galling and wear
● High compressive strength
Ductile iron casting
Ductile iron or ductile iron obtains its special properties by adding magnesium to the alloy. In contrast to grey cast iron, the presence of magnesium causes the graphite to form an ellipsoid. Ingredient control is very important in the manufacturing process. If impurities react with magnesium the shape of the graphite molecules will be affected. Different grades of ductile iron are formed by manipulating the microcrystalline structure. This is achieved by casting or by heat treatment.
● Very high ductility & strength
Compacted graphite iron casting
Compacted graphite iron has a graphite structure and related properties, and is a mixture of grey iron and white iron. The microcrystalline structure is formed around interconnected blunt graphite flakes. An alloy such as titanium is used to suppress the formation of spherical graphite. Compared with grey cast iron, it has higher tensile strength and higher ductility. The crystallite structure and properties can be adjusted by heat treatment or by adding other alloys.
● High tensile strength
● Good elongation properties
Malleable iron casting
White iron can be further processed into malleable cast iron through a heat treatment process. The extended heating and cooling procedures will cause the iron carbide molecules to decompose, releasing free graphite molecules into the iron. Different cooling rates and the addition of alloys will produce malleable cast iron with a microcrystalline structure.
● High ductility
● Tougher than grey cast iron
● Twists and bends without fractures
● Excellent machining capabilities
● Good casting properties
● Good machinability
● Low Cost
● Strong compression strength compared to steel
● Excellent anti-vibration properties
● Good Sensibility
● Excellent resistance to wear
● Constant Mechanical properties between 20 to 350 degree Celsius
● Low stress concentration
● Durability and resistance to deformation
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